1. Technical Field
This invention relates generally to data communications, and in particular to data communications in a Local Area Network (LAN). Specifically, the invention is directed to managing wireless access to a LAN.
2. Description of the Related Art
The need for personal wireless communications is expanding rapidly with the advances in digital communications and personal communications systems. The progress in wireless radio technology and the growth rate of the wireless telephone systems over the last several years is indicative of tremendous market demand for location independent communication via wireless access. Many of the current wireless networks architectures are primarily designed and optimized for voice communications and wide area coverage. With the proliferation of personal and portable computers, and local area networks, it is envisioned that data services and applications such as file server access, client-server execution, and electronic mail will require wireless access to the LAN environment supporting distributed computing. The use of wireless communication systems to transmit data traffic utilizing mobile devices which communicate with a hardwired network, such as a LAN or a wide area network (WAN), has become widespread. A mobile worker can be connected everywhere on an office building or business campus, which translates into increased productivity. Retail stores and warehouses, for example, may use wireless communications systems with mobile data terminals to track inventory and replenish stock. The transportation industry may use such systems at large outdoor storage facilities to keep an accurate account of incoming and outgoing shipments. In manufacturing facilities, such systems are useful for tracking parts, completed products and defects. Since the characteristics and profile of data traffic are very different from those of voice traffic, the wireless access protocol must efficiently accommodate the very dynamic and bursty nature of data traffic.
A typical wireless communications system includes a number of fixed access points (also known as base stations) interconnected by a cable medium often referred to as a system backbone
Associated with each access point is a geographic cell. The cell is a geographic area in which an access point has sufficient signal strength to transmit data and receive data from a mobile device such as a data terminal or telephone with an acceptable error rate. Typically, access points will be positioned along the backbones such that the combined cell area coverage from each access point provides full coverage of a building or site. For 802.11(b), an access point provides 11 Mbps, which is shared by a number of users. In the case of WLAN, frequently there is significant overlaps in cells to increase data capacity, since the capacity of the network is a function of the number of access points. So a user typically has access to several different access points in any given location.
Mobile devices such as telephones, pagers, personal digital assistants (PDA's), data terminals etc. are designed to be carried throughout the system from cell to cell. Each mobile device is capable of communicating with the system backbone via wireless communication between the mobile device and an access point to which the mobile device is registered. As the mobile device roams from one cell to another, the mobile device will typically deregister with the access point of the previous cell and register with the access point associated with the new cell.
Recently a standard for wireless local area networks (WLANs) known as the IEEE 802.11 standard has been adopted and has gained acceptance among the industrial, scientific and medical communities. The IEEE 802.11 standard for WLANs is a standard for systems that operate in the 2,400–2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. The IEEE 802.11 RF transmissions use multiple signaling schemes (modulations) at different data rates to deliver a single data packet between wireless systems. The latest IEEE 802.11 wireless LAN uses a band of frequencies near 2.4 Ghz for direct sequence spread spectrum transmissions. Another recently adopted short-range standard has evolved known as the Bluetooth standard (see www.bluetooth.com). The Bluetooth standard is a low-cost short range wireless connection which uses much of the same range of frequencies for its frequency-hopping spread spectrum transmissions as the IEEE 802.11 standard. In some applications, it is appropriate to use systems employing IEEE 802.11 concurrently with other systems using the Bluetooth standard.
In IEEE 802.11 wireless LAN technology, there is a shared transmission medium between the access point and client devices. Since an access point can only be receiving data from one client at a time, a given client can monopolize that channel, effectively reducing throughput available to other clients. So, for example, clients that request bandwidth often, may be granted a disproportionate amount of bandwidth. This problem is further exasperated by the fact that WLAN is a data packet based technology. With digital cellular systems, transmissions are connection based, so the digital cellular setup circuit can guarantee bandwidth to the client. For WLAN clients, data transmissions are bursty in nature, so bandwidth throughout a transmission cannot be guaranteed. Accordingly, there is a strong need in the art for a system and method that prevents a single client on the wireless LAN from monopolizing the network bandwidth.